Charged particle beam apparatuses are used in a plurality of industrial fields. Testing of semiconductor devices during manufacturing, exposure systems for lithography, detecting devices and inspection systems are some examples of these fields.
In general, there is a high demand for structuring and inspecting specimens within the micrometer or nanometer scale. On such a small scale, process control, inspection or structuring is often done with charged particle beams, e.g. electron beams, which are generated and focused in charged particle beam devices, such as electron microscopes, electron beam pattern generators or charged particle inspection systems. Charged particle beams offer superior spatial resolution compared to e.g. photon beams due to their short wavelengths.
However, for a given beam diameter, the charged particle beam current limits the throughput of charged particle beam systems. Since further miniaturization of e.g. structures to be imaged is necessary, the charged particle beam diameter has to be decreased. As a result, the beam current for individual beams, and thus the throughput, is decreased.
In order to increase the total charged particle beam current, thus increasing the throughput, a plurality of charged particle beams can be used. In this manner, the throughput can be increased proportional to the number of columns in a multi-column system.
One option for obtaining a plurality of charged particle beams may be combining several single beam columns with each other. However, some components, especially magnetic lenses, cannot be miniaturized sufficiently, since the magnetic field cannot be arbitrarily increased. Thus, the columns have to be spaced such that the distance between electron beams is 100 mm to 200 mm.
To overcome this problem, U.S. Pat. No. 3,715,580 utilizes a magnetic lens with a circular excitation coil providing two holes, each for a single electron beam. Thereby, the continuous rotational symmetry of previous lenses is abandoned since the hole (optical axis) for each electron beam has different distances from the position of the excitation coil. This lack of symmetry of the magnetic focusing field results in additional aberrations, and thus reduces the obtainable resolution.
Further, U.S. Pat. No. 7,576,917 describes a multi-axis lens with identical individual sub-units. The multi-axis lens allows close packing of lenses in a one dimensional array, but there remains a desire to reduce the spacing even further. Especially with the multi-axis lens, the spacing to a neighboring second array remains large.
Since there is a strong desire for improving resolution, for simplifying manufacturing and for minimizing aberrations in such systems, it is an object of the present invention to further improve state of the art devices.